Highly photocatalytic activity of pH-controlled ZnO nanoflakes

ZnO nanoflakes were successfully synthesized by the sol-gel method at a precursor solution pH of 13. The structure, morphology, and photocatalytic activity of the synthesized ZnO nanoflakes were characterized using X-ray diffraction, scanning electron microscope, and ultraviolet–visible spectrophotometer, respectively. The ZnO nanoflakes were highly crystalline semiconductors with an optical band gap of 3.27 eV. The ZnO catalysts revealed a remarkable photocatalytic efficiency toward the degradation of organic dyes including methylene blue (MB), methylene orange (MO), congo red (CR), and rhodamine B (RhB) under UV irradiation. Moreover, the influence of solution pH on photocatalytic activity was also investigated. It was found that the photocatalytic efficiency increased in response to the increase of pH values by degradation of MB, MO, and RhB. However, upon the decrease in pH value, the photocatalytic degradation efficiency of CR was increased. The best result was recorded on the photodegradation of CR with a maximum efficiency of 100% at a pH value of 4 for 10 min.